The present invention relates to an improved hearing aid and more particularly to a hearing aid in which the frequency response is controllable over a wide range for better establishing the response of the hearing aid to the hearing of the wearer.
Prior art hearing aids include a small amount of adjustment with respect to frequency response of the hearing aid system. The hearing aid industry has recognized for some time that hearing aid characteristics with respect to frequency response need to cover a wide range in order to accurately correct for hearing problems of the wearers of hearing aids. However, it has been difficult to provide a sufficiently wide range of response within a single hearing aid. Therefore, different hearing aid models have been produced for different ranges in order to provide the user with a model best suited for his particular hearing condition. The normal frequency spread for hearing is frequencies in the range of 150 hertz to 7,000 hertz.
The biggest hearing loss of users is due to aging. This bearing loss for the average person occurs in the high frequency range. Therefore, audio signals in the high frequency range need to be amplified relative to signals in the low frequency range. With some people a small amplification of high frequency signals is needed; with others a large amplification is necessary. Also, it has been found that the transition where the hearing loss occurs is a sharply defined transition, generally in 1-2 kilohertz range.
With these problems in mind, it is highly desirable to find a hearing aid system which has its frequency response controllable over a wide range. More particularly, it would be highly advantageous if such a wide range of frequency response were adjustable by a single control.
Therefore, it would be highly desirable to provide a circuit which provides an adjustable relationship of gain of the high end relative to the low end of the audio frequency spectrum by adjustment of a single control. Such a circuit must operate within the volume confines of a normal hearing aid and be suitable for a wide variety of hearing losses.
It is therefore an object of the present invention to improve the frequency shaping characteristics of a hearing aid over the present state of the art for the purpose of achieving a closer match of hearing aid frequency response to the desired frequency response of the wearer of the aid, and to do it with the minimum of discontinuities or glitches in the frequency response.
It is yet another object of the present invention to provide a circuit that yields a wide range of frequency response in accordance with the adjustment of a single control.